1. Field of the Invention
The present invention relates to an apparatus for heating parts of thermoplastic material by at least partial irradiation using a heat radiator located in a quartz tube. More particularly, the present invention relates to an apparatus comprising an electrical resistance wire which can be connected at both its ends to a power supply and a heat-resistant element for securing the quartz tube at least in the region of its tube end The present invention also relates to a method for shaping a thermoplastic part.
2. Description of the Related Art
German reference DE 28 54 393 A1 discloses a process in which thermoplastic or thermoelastic semifinished products are arranged at a suitable distance from a heat radiator until the shaping temperature is reached. The thermoplastic semifinished product at shaping temperature is formed into a desired shape in a manner known in the art. Infrared radiators are used to generate the thermal radiation.
German reference DE-A 16 04 607 discloses an apparatus for welding layers of films of thermoplastic material using an electrical heat radiator, i.e., an electrical resistance wire in a quartz tube. In this case, the electrical heat radiator is provided with a water cooled copper alloy bar of high thermal conductivity. The bar has a slot on its side directed toward the films to be welded which extends over the length of the radiator, the width of which determines the width of the weld. The bar is likewise open on its side facing away from the films to be welded and is provided with an outer reflection layer, in particular with a gold coating.
Swiss Patent 407 357 also discloses a quartz glass flow tube which has electrical heating conductors in its interior. The quartz glass flow tubes are designed in the form of pipe coils or quartz tube helixes.
In these references, the semifinished products to be treated are generally sheet-like formations or liquid substances; it is not intended for the thermal radiation to be concentrated on semifinished products of plastic material having a definite shape.
The object of the present invention is to heat small parts of plastic material, at least partially, by means of irradiation up to the softening point, and subsequently mechanically shape or connect them to one another. Such small parts might include, for example, plastic rivets.
The present invention provides a quartz tube designed in the form of a helix.
The helix is adapted so that it can be pushed along its axis onto a body of plastic material by means of an element serving as a securing means.
In an embodiment of the present invention, a multiple helix apparatus is used for simultaneous rapid low cost heating of a plurality of plastic parts.
In a further embodiment of the present invention, a resistance wire is preferably connected both electrically and mechanically at both ends to stripped ends of a temperature resistant stranded wire inside the quartz tube.
In a preferred embodiment, a heating conductor spiral of an Fe/Cr/Al alloy is located in the quartz tube designed as a helix or pipe coil. The quartz tube helix is held at both ends by a heat resistant element. The heat resistant element, has, in this case, an elongated clearance, the longitudinal axis of which runs parallel to the helix axis of the quartz tube coil. The clearance is preferably formed as a drilled hole.
In a further embodiment of the present invention, the apparatus may be used, for example, in the installation of subassemblies in automobiles as part of a handling system. The apparatus is advantageous, here, in particular, due to its small dimensions.
In a further embodiment of the present invention, a reflection layer is provided in the region of the outer circumference of the helix.
In a preferred embodiment, the quartz tube helix is provided with a reflective layer on its outer side facing away from the helix axis. Preferably, the reflective layer is a gold layer applied on the outer surface of the quartz tube. This allows a relatively high energy yield to be achieved.
Another object of the present invention is to provide a simple and rapid method of shaping plastic pins into rivets by means of a compact, easy to guide heating apparatus.
The present invention provides a method of shaping a pin shaped body of plastic material, at least with respect to the part to be shaped, by heating it to shaping temperature using a quartz tube heating element as defined herein. The quartz helix is pushed at least partly onto the body of plastic material along the helix axis, and heated by a securing means. The pin shaped part may then be shaped, for example, into a rivet head, by using a rivet forming die which is moved in relation to the body of plastic material.
In an embodiment of the present invention a method for shaping at least two parts of a body of plastic material is provided including heating the plastic material to shaping temperature using at least two apparatuses. The bodies of plastic material to be shaped are designed in the form of pins, at least at the part intended for shaping. The quartz helix of each apparatus is pushed at least partly onto the respective body of plastic material and heated by a securing means. The pin shaped parts may then be shaped, for example, into a rivet head by pressing a rivet forming die onto the heated plastic part.
In an embodiment of the present invention, the process is performed with the aid of a handling apparatus.